On Thu, 2006-08-10 at 22:13 +0100, Duncan Coutts wrote:
So, with this in mind, can we come up with a syntax & semantics that is close to our current configurations proposals but is not evil?
One thing that might help is if we split the 'package' condional test into two distinct things. I think we're using it for different purposes which correspond roughly to Gentoo's "dep || dep" xor dep syntax and it's "flag? dep" syntax. In one case it's an inconsequential decision to pick one dep, we use the other when the user might legitimately want to control if the dependency is used. So perhaps we could have 'package'(dependecy) and 'use'(dependency). I'll try and explain what both mean. 'package' conditionals would be for selecting things depending on which version of a package we depend on ends up getting used. 'use' conditionals would be for selecting optional dependencies from the environment. These would get corresponding --enable-foo --disable-foo configure flags, though would default depending on the presence of the package. So, examples: -- if the base package is <2.0, depend on fps: build-depends: base configuration: package(base < 2.0) build-depends: fps>=1.0 ghc-options: -DUSE_OLD_FPS -- optional gui build-depends: base configuration: use(gtk) && use(cairo) build-depends: gtk, cairo ghc-options: -DUSE_GUI I'm not sure that's ideal when we need to depend on multiple optional packages. Maybe something like this'd be nicer flag: debug default: False flag: gui default: use(gtk >= 0.9.10) && use(cabal >= 0.9.10) configuration: flag(gui) build-depends: gtk, cairo ghc-options: -DUSE_GUI configuration: flag(debug) ghc-options: -DDEBUG -O0 configuration: !flag(debug) ghc-options: -O2 -funbox-strict-fields So we have a flag with a reasonable default value but all flags can be manually overridden. I'm still concerned that the order of configurations is significant: build-depends: base flag: debug default: False configuration: flag(debug) build-depends: HUnit>=1.0 configuration: package(HUnit>=1.1) ghc-options: -DBlah Since we do not know which packages we're depending on 'til we've dealt with the first configuration. So looking at them in a different order would give different results. Perhaps we just live with it and say that they get done in order. There's still the possibility that we put all build-depends upfront: flag: debug default: False build-depends: base, flag(debug)? ( HUnit>=1.0 ) configuration: package(HUnit>=1.1) ghc-options: -DBlah So I think I'm suggesting that we explicitly specify flags and give them default values which may be based on the environment. Then deps are specified in terms of those flags, and os/arch. Then configurations can be conditional on flags, os/arch, and versions of packages that we're actually going to build with. Duncan